PLANT PHYSIOLOGY , Vol 109, Issue 2 579-585, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Sucrose Release into the Endosperm Cavity of Wheat Grains Apparently Occurs by Facilitated Diffusion across the Nucellar Cell Membranes
N. Wang and D. B. Fisher
Department of Botany, Washington State University, Pullman, Washington 99164-4238
Nutrients required for the growth of the embryo and endosperm of developing
wheat (Triticum aestivum L.) grains are released into the endosperm cavity
from the maternal tissues across the nucellar cell plasma membranes. We
followed the uptake and efflux of sugars into and out of the nucellus by
slicing grains longitudinally through the endosperm cavity to expose the
nucellar surface to experimental solutions. Sucrose uptake and efflux are
passive processes. Neither was sensitive to metabolic inhibitors, pH, or
potassium concentration. p-Chloromercuribenzene sulfonate, however,
strongly inhibited both uptake and efflux, although not equally. Except for
p-chloromercuribenzene sensitivity, these characteristics of efflux and the
insensitivity of Suc movement to turgor pressure are similar to those of
sucrose release from maize pedicels, but they contrast with legume seed
coats. Although the evidence is incomplete, movement appears to be carrier
mediated rather than channel mediated. In vitro rates of sucrose efflux
were similar to or somewhat less than in vivo rates, suggesting that
transport across the nucellar cell membranes could be a factor in the
control of assimilate import into the grain.
